This application relates to the production of polymeric carbon materials, particularly glassy carbon materials for use, e.g. in electronic components and high temperature materials applications.
Carbon materials synthesized from organic materials have found utility in a wide range of applications including the aerospace, sporting goods, electronic and automotive industries. The organic polymer is heated to a temperature, e.g. 900.degree. C., sufficient to cause charring of the material to form the carbon product. For applications involving molded products, it is desirable that the weight loss on charring be sufficiently low (generally less than 15%) to avoid fracture of the molds or formation of cavities in the final monolithic material. Further, for use in molding the polymeric material should exhibit a well defined melting point prior to conversion to the carbon material (i.e., prior to charring) so that it can be drawn into the mold in a molten state during processing. A flow or melting event during processing is necessary to produce a solid monolithic product of glassy carbon upon thermal treatment. Materials without a well defined melting point tend to form powders on charring which are useful in non-molded applications. See Fitzer, E. Pure & Appl. Chem. 52, 1865-1882 (1980); Fitzer, E. in Contemporary Topics in Polymer Science 5, Vandenberg, E. J. ed., Plenum, N.Y. 1984, pp 101-138.
It is known that glassy carbon material can be made by a process involving the steps of
(1) synthesis of 1,3-diethynylbenzene from 1,3-diacetylbenzene; PA0 (2) polymerization of the 1,3-diethynylbenzene with a Ni catalyst, making sure to stop the polymerization prior to insolubility; PA0 (3) addition of low molecular weight oligomers to such as acetylenically substituted aromatic compounds, to help flow; PA0 (4) preheating to 170.degree.-200.degree. C.; and PA0 (5) heating the material to 900.degree. C. in a nitrogen atmosphere to form a glassy carbon material. See U.S. Pat. No. 4,070,333 incorporated herein by reference. PA0 (a) polymerizing 1-bromo-4-lithiobenzene to form a brominated polyphenylene wherein the ratio of brominated to non-brominated residues in the polymer is 1:5 or greater; PA0 (b) functionalizing the brominated polyphenylene to replace the bromide groups with a substituted or unsubstituted acetylene group; and PA0 (c) heating the functionalized polymer to a temperature of 900.degree. C. in an atmosphere to form polymeric carbon. Preferably, the brominated polyphenylene is formed in an ethereal solvent such as tetrahydrofuran and then functionalized using a palladium catalyst and a copper catalyst. When the acetylene substituent is phenylacetylene, the product of the method is glassy carbon.
It has also been suggested that an oligophenylene-derived material with terminal alkyne groups is a suitable starting material for making isotropic polymeric carbon. Fitzer, E., Pure Appl. Chem. 52, 1865 (1980). This material does not provide the melting event necessary to the making of monolithic products, although it does have a high char yield.
The present invention provide an alternative process for making carbon materials with a high char yield. A preferred embodiment combines this high char yield with a distinct melting event prior to the formation of the carbon material.